Finned heat exchanger tubing and method of manufacture thereof



July 29, 1969 T, M, RQHDE 3,457,756

FINNED HEAT EXCHANGER TUBING AND METHOD OF MANUFACTURE THEREOF Filed Oct. 12, 1967 2 Sheets-Sheet 1 INVENTOR.

THEODORE M. ROHDE Hl$ ATTORNEY July 29, 1969 1'. M. ROHDE FINNED HEAT EXCHANGER TUBI NG AND METHOD OF MANUFACTURE THEREOF Filed Oct. 12, 1967 I 2 Sheets-Sheet 2 FIGS INVENTOR.

THEODORE M. ROHDE BYz/ w 2 2 H S ATTORNEY United States Patent 3,457,756 FINNED HEAT EXCHANGER TUBING AND METHOD OF MANUFACTURE THEREOF Theodore M. Rohde, Fern Creek, Ky., assignor to General Electric Company, a corporation of New York Filed Oct. 12, 1967, Ser. No. 674,897 Int. Cl. B21d 35/00, 53/08; F28f 1/16 U.S. Cl. 72-186 Claims ABSTRACT OF THE DISCLOSURE A finned heat exchanger tubing is made from a length of stock comprising a tube having a longitudinally extending flange by corrugating the flange to increase its surface area, cutting the corrugated flange to form fins and twisting and shaping the fins so that in the final product the fin end portions are substantially perpendicular to the tubing axis and the corrugations therein are partially ironed out.

Background of the invention Heat exchangers comprising a tubular passageway for containing a heating or cooling medium or means are usually provided with fin means for increased heat transfer surface exposed to the surrounding atmosphere. For maximum heat exchange effectiveness, the fin means must be in intimate heat conducting contact with the passageway and should be shaped to provide an optimum balance between its heat transfer effectiveness, which is a function of its surface area, and its heat conduction properties which is dependent on its cross-sectional area.

A simple and relatively low cost means for producing a heat exchanger tubing having an extended surface integral therewith comprises the extrusion of an aluminum alloy or other extrudable metal in the form of a continuous tubular passage having one or more longitudinal flanges extending outwardly from the passageway wall. However, the flat, continuous flanges do not provide good heat transfer contact with the surrounding atmosphere. Also, the total heat transfer or surface area of the flange is low as compared with its heat conducting or cross-sectional area.

These deficiencies of such flanged tubular stock have long been recognized and various treatments of the flanges have been used or proposed for the purpose of improving the heat transfer properties. For example, Patent 2,347,957-McCullough teaches the idea of ruifling or corrugating the flange edge to increase its surface area and also to provide a more turbulent, and hence more efiicient, contact of the air currents flowing across the flange. In Patent 2,963,779-Mosgard-Jensen, the flange is slit to provide individual fins and these fins are alternately bent in opposite directions from the original plane of the flange to promote a greater turbulence of the ambient atmosphere passing through the fins and to induce a better heat exchange contact between the heat exchange surfaces and the atmosphere. In Patents 2,286,27l-Higham and 3,- 294,1 62J oehlein et al., the extruded flange is slit transversely to form a plurality of fins and these fins are twisted to an angle relative to the axis of the tubular portion or, as is specifically taught in the Loehlein et al. patent, are also drawn or ironed by the pressure of cooperating gear means to increase the surface area thereof over the original surface area of the flange.

Summary of the invention In accordance with the present invention a multiple fin heat exchanger is manufactured from extruded or otherwise formed stock comprising a hollow tubular member having at least one continuous longitudinally extending flange by an improved method designed to produce 'ice from the flange, a fin structure which not only has a surface area substantially greater than the area of the original flange but is also characterized by individual fins of an irregular rippled surface configuration providing intimate heat exchange contact with the air or other gas passing over the fin surfaces.

Briefly described, the method of the present invention comprises fluting or corrugating the flange to obtain a 1ongitudinal stretching thereof, dividing the fluted flange into a plurality of fins, each of which preferably comprises at least one complete flute or corrugation, and twisting the outer end portions of the fins to an angle of preferably about relative to the longitudinal axis of the tubing. Preferably, the method also includes an ironing of the end portions to partially flatten the flutes or corrugations. The resultant irregular or rippled fin surfaces promote an increased turbulent air flow condition as compared with relatively large flat smooth surfaces and thus provide an efiicient scrubbing of the fin surfaces by air or other gas circulated over the fins.

Brief description of the drawing In the accompanying drawing:

FIGURE 1 is a perspective view illustrating one embodiment of the present invention and apparatus suitable for carrying out certain steps employed in the practice of the method of the invention;

FIGURE 2 is a fragmentary side elevational view showing the operating positions of certain components of the apparatus in an intermediate stage of the operation thereof;

FIGURE 3 is a top fragmentary view of a portion of the apparatus of FIGURE 1;

FIGURE 4 is a partial sectional view taken generally along lines 4-4 of FIGURE 2 showing the operating positions of certain components of the apparatus in an ini tial stage in the manufacture of the finned tubing;

FIGURE 5 is a view similar to FIGURE 4 showing the same elements in a later stage of operation; and

FIGURE 6 is a sectional view illustrating another embodiment of heat exchanger tubing of the present inventi-on.

Description of the preferred embodiments While the stock employed in the practice of the present invention may be produced by any suitable method the invention will be particularly described with reference to a commercially available, extruded blank or stock comprising, as is shown in the right hand portion of FIG- URE 1, a continuous hollow tubular portion 1 and longitudinally extending and coplanar flanges 2 integrally connected to the tubular portion 1.

The fiat flanges are first fluted or corrugated laterally, or in other words with the corrugations extending across the width of the flanges, to effect a substantial increase in the surface areas of the flanges. This step may conveniently be carried out by passing each flange through a set of serrated rollers including an upper roll 3 and a lower roll 4. The intermeshing teeth 5 and 6 of the sets of rolls are designed to corrugate each of the flanges to a fluted shape indicated by the numeral 7. The depth of these corrugations and the sizes or widths thereof are not particularly critical provided that the flanges are deformed or stretched sufliciently to provide a substantial increase in the area of the flanges, for example a 20% increase, without actual tearing of the flange material.

The corrugated or fluted flanges 7 are then cut or lanced laterally substantially to the base of the flanges as illustrated by the numeral 10 in FIGURE 3 of the drawing to provide a plurality of radially extending fins 11 each of which, as is shown in FIGURE 2 of the drawing, contains at least one complete flute or corrugation, that is a corrugated section including at least one crest 12 and one valley or depression 14.

In the next step, the corrugated fins 11 are subjected to additional mechanical working involving the twisting of the fin ends through an angle of about 90 and, preferably also, an ironing of the corrugated fin surfaces to remove most, but not all, of the corrugations.

In the use of the apparatus illustrated in the drawing, the cutting, twisting and ironing steps are all effected by rotary or flying scissor means.

These means include a pair of coaxial disks 15 and 16 operatively positioned with reference to each corrugated flange. The disks of each pair are designed to rotate in opposite directions and are provided with radially extending blades or elements 17 and 18 respectively mounted on the peripheries thereof. One of these elements, specifically the element 18 includes a cutting edge 19 for laterally lancing the corrugated flange 7. More specifically, as is shown in FIGURE 2 of the drawing, this cutting element 18 is arranged to strike the upper surface of a corrugated flange 7 while this flange is supported on a mandrel 20 and to move downwardly through the corrugated flange as it severs a fin 11 from the corrugated flange 7.

The rotations of the disks 15 and 16 in opposite directions are synchronized so that at approximately the same time that the scissor element 18 engages one side of the flange to lance a fin therefrom, the other element 17 engages the forward edge 21 of the newly formed fin and as the two elements move past one another, they cooperate to provide a twisting of the fin about its axis.

To facilitate the twisting action, each of the elements 17 and 18 includes slanting wall portions 22 which cam the opposite side edges of the fin 12 towards a 90 displacement of the fin edge portion.

Ironing of the twisted fin to increase the overall width of the fin is primarily effected by the opposed flat surfaces 23 of the respective elements 17 and 18 which pass one another in the plane of the original flange, or in other words, at a point at which the rotated or twisted fin is contained between these two surfaces 23.

The lancing or cutting and ironing operations are particularly illustrated in FIGURES 4 and 5 of the drawing. From FIGURE 4 it will be noted that the two elements engage the corrugated flange 7 at about the same moment although it may be desirable that the lancing element 18 perform its lancing operation before any substantial twisting action has resulted from engagement of the element 17 with the new fin 11. After the new fin has been severed from the corrugated flange 7 and twisted, the flat surfaces 23 of the two elements 17 and 18 pass one another as shown in FIGURE 5 of the drawing and confine the fin to the limited space provided between the two flat surfaces 23 to thereby forcibly iron or draw the fin so that the corrugations are substantially flattened to relatively shallow ripples. Preferably the space between the two surfaces 23 of the respective elements 17 and 18 is only slightly wider than the actual thickness of the fin in its uncor-rugated form so that while the corrugations are substantially flattened, there is sufficient space to permit the elements to pass without binding.

The radial or longitudinal shape of the elements 17 and 18, particularly the element 18, are such that they will clear, as shown in FIGURE .3, the unbent portions of the fins 12 during their operation and at the same time provide the depth of cut necessary for lancing the fin from the corrugated flange 7. At least the blade 18 must be provided with a flat surface 26 on the side thereof facing the uncut flange 7 and a slanting portion 27 on the opposite side and extending from the tip of the blade in order to clear the flange 7 and the base section 28 of the newly cut fin 11. Element 17 is illustrated as being of It will be obvious, of course, that the method steps need not be combined in the operation of the single apparatus such as that illustrated. For example, the flanges may be corrugated in one machine, cut into fins in a second machine and thereafter, in a third machine, subjeoted to a fin twisting and shaping operation. However, when one piece of apparatus is employed for carrying out all three operations, the corrugating gears or rollers 3 and 4 may also be employed to feed the stock to the scissors means at the required rate, which is, of course, the advancement of the stock one fin width between the times in which the cutting elements 17 and 18 perform their cutting and forming operations.

It will be understood, of course, that the final product may include one or more sets of fins. For example, FIGURE 6 illustrates in cross-section an embodiment of the product of the present invention in the form of a tubular passage 32 including four equally spaced sets of fins- 33. It will be obvious, of course, that this structure is manufactured from an extruded or otherwise formed flanged tubular stock including four equally spaced longitudinal flanges.

The final fin shape and surface structure is illustrated in the left hand portion of FIGURE 2 and in FIGURE 6. Its end portion indicated by the numeral 34 is of a somewhat irregularly rippled shape. More specifically, while the fin end portion 34 still exhibits the remains of the corrugations provided by the serrated rollers 5 and 6, the corrugations are substantially but not completely ironed out, at least along the end of the fin, but at no point along the fin length, except at its very base section is the fin absolutely smooth or flat.

The intermediate section of the fin, that is, the section 35 which includes the actual twisted portion of the fin may retain some of the original corrugated structure due to the fact this part of the fin may not be ironed, or completely ironed, by the blades 17 and 18.

As the ends of the fins 34 are substantially perpendicular to the longitudinal axis of the tube 2, the finned tube of the persent invention lends itself particularly to the production of heat exchangers such as refrigerant condensers or evaporators comprising a plurality of spaced parallel passes of tubing interconnected by end turns. Air flow through such structure in a path normal to the passes is not significantly deflected by the fins so that there is a minimum pressure drop in the heat exchanger structure. Thus the heat transfer rate is maximized with minimum imposed air pressure drop. In addition, the twist provides a fin spacing and alignment best suited to tolerate the front build-up associated with the evaporator operation between defrost cycles.

The flanged stock used in the practice of the present invention need not be an extruded stock as it could be formed from two flat sheets or ribbons by a roll bonding process as described in Long Patent 2,662,273 and Grenell Patent 2,690,002.

It will also be obvious that, within limits, by changing the relative speed of the blades with respect to the linear stock feed and an accompanying change in blade geometry, the apparatus may be easily adapted to form fins of different widths and spacing.

While the invention has been described with reference to certain embodiments thereof, it will be understood that it is not limited thereto and it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making finned heat exchange tubing which comprises:

providing a passage for containing a heating or cooling means having a longitudinally extending flange as an integral part thereof;

corrugating said flange laterally to increase the surface area thereof;

dividing said corrugated flange into a plurality of fins;

and twisting said fins to position the outer end portions thereof at an angle relative to the longitudinal axis of said tubing.

2. The method of claim 1 including the additional step of partially flattening the corrugated end portions of said fins.

3. The method of claim 1 in which said fins are twisted to an angle of about 90 relative to said longitudinal axis.

4. The method of claim 1 in which the divided fins each include at least one complete corrugation.

5. The method of making finned heat exchange tubing which comprises:

providing a length of tubing having a longitudinally extending flange as an integral part thereof;

fluting at least the outer edge of said flange;

dividing said fluted flange into a plurality of fins;

twisting the outer end portions of said fins to an angular position of about 90 relative to the longitudinal axis of said tubing;

and ironing said end portions of said fins to at least partially flatten and widen said flutes. 6. The method of claim 5 wherein said dividing, twisting and ironing steps are provided substantially simultaneously by rotary scissor means and said fins are of a width such that each fin includes at least one complete corrugation.

7. A method of making a heat exchanger comprising the steps of providing a length of tubing having a longitudinally extending flange formed as an integral part thereof;

advancing said flange into the paths of cooperating shearing and forming means moving in opposite parallel paths substantially perpendicular to the plane of said flange and spaced from one another a distance slightly greater than the thickness of said flange;

synchronizing the movement of said forming means so that, as one of said forming means engages one surface of said flange and shears said flange along a transverse line to form a fin and passes through the plane of said flange to twist at least the adjacent end portion of said fin to an angular position, the other of said forming means engages the opposite side edge of said fin to twist the remaining end portion of said fin to the same angular position.

8. The method of making a heat exchanger comprising a tubular member having a plurality of longitudinally aligned twisted fins integral with said member from a flanged tubular stock in which said flange extends longitudinally of the tubular portion thereof, which method comprises:

laterally corrugating said flange;

contacting One surface of said corrugated flange by a moving cutting element adapted to laterally shear said flange to form a fin and to pass through the plane of said flange and apply a twisting force to the adjacent edge of said fin;

simultaneously contacting the Opposite edge of said fin by a forming element traveling in a path parallel to and in the opposite direction from said cutting element and adapted to pass through the plane of said flange concurrently with said cutting element and to apply to said opposite edge a twisting force opposite that applied by said cutting element;

the space between the passing cutting and forming elements being such that the end portion of said fin is twisted approximately relatively to the base portion thereof and the corrugations therein are partially ironed out, thereby widening the flute.

9. A heat exchanger tubing comprising a tubular member having a plurality of longitudinally aligned fins integral with said member,

each of said fins comprising a longitudinally extending base portion, a corrugated intermediate twist portion and an end portion positioned at a substantial angle relative to said base portion,

at least the end portions of said fins having a rippled transverse surface configuration.

10. The tubing of claim 9 in which said angle is about 90. References Cited UNITED STATES PATENTS 5/1944 McCullough 29l57.3 5/1946 Brown 29157.3 

